A turbomachine, such as a gas turbine, generally includes an inlet section, a compressor section, a combustion section that includes a plurality of combustors, a turbine section and an exhaust section. The inlet section cleans and conditions a working fluid (e.g., air) and supplies the working fluid to the compressor section. The compressor section progressively increases the pressure of the working fluid and supplies a high pressure compressed working fluid to a compressor discharge casing that at least partially surrounds each of the combustors.
A fuel is mixed with the high pressure compressed working fluid and the mixture is burned in a combustion chamber that is defined within each combustor to generate combustion gases having a high temperature and pressure. The combustion gases flow along a hot gas path defined within the compressor discharge casing and into the turbine section where they expand to produce work. For example, expansion of the combustion gases in the turbine section may rotate a shaft connected to a generator to produce electricity.
The hot gas path is at least partially defined by an annular combustion liner and/or a transition duct. The transition duct may be provided as part of a transition piece assembly. A conventional transition piece assembly includes an outer impingement sleeve that circumferentially surrounds the annular transition duct. A cooling annulus is defined between the outer impingement sleeve and the transition duct. A downstream end of the transition piece assembly terminates at an inlet port to the turbine.
An aft frame or support member extends generally radially outward and circumferentially around the downstream end of the transition piece assembly. Typically, the aft frame is mounted to a casing, an inner support ring and/or to the turbine so as to provide mounting support for the transition piece assembly and to reduce deformation of the transition duct. During operation, the aft frame is exposed directly to the hot combustion gases. As a result, various cooling schemes have been developed to enhance the thermal and mechanical performance of the aft frame.
One conventional cooling scheme includes routing a portion of the high pressure compressed working fluid from the compressor discharge casing through one or more cooling passages defined within the aft frame and exhausting the high pressure compressed working fluid into the hot gas path and/or into the cooling annulus. The exhausted compressed working fluid may then be used to cool the transition duct and/or the combustion liner. In addition, the compressed working fluid may be routed through the cooling annulus towards the combustion chamber for mixing with the fuel for combustion.
One limitation of conventional cooling schemes is that the shape and/or complexity of the internal cooling passages are limited to single pass or generally linear cooling channels within the aft frame. For example, conventional cooling passages a generally linear inlet port that feeds cooling air to a linearly cooling channel and out of the aft frame through an exhaust port. This linear or single run of the compressed working fluid through the cooling channel restricts the cooling capacity of each cooling channel. In addition, current manufacturing processes require expensive and time consuming secondary operations such as milling or electrical discharge machining to cut the cooling passages and/or the inlet ports and the outlet ports into the aft frame, thus increasing costs of manufacturing.
A second limitation of existing cooling schemes may be prevalent where there is an obstruction such as a fuel injector or other bluff body within the cooling annulus, thus resulting in measurable pressure losses of the high pressure compressed working fluid between the aft frame exhaust ports and the combustion chamber. Another potential limitation of existing cooling schemes may be that the location and orientation of the exhaust ports may not provide optimized cooling beyond the aft frame area. Therefore, an improved internally cooled aft frame for a combustor of a turbomachine, such as a gas turbine, would be useful.